public class test3 {
    //力扣  852.山脉数组的峰顶索引
    public int peakIndexInMountainArray(int[] arr) {
        if(arr.length==0){
            return 0;
        }
        int left = 0,right = arr.length-1,mid = 0;
        while(left<right){
            mid = left + (right - left +1)/2;
            if(arr[mid]>arr[mid-1]){
                left = mid ;
            }else {
                right = mid-1;
            }
        }
        return right;
    }
}
